class Ractor - RDoc Documentation (original) (raw)

Ractor is a Actor-model abstraction for Ruby that provides thread-safe parallel execution.

Ractor.new can make new Ractor and it will run in parallel.

r = Ractor.new {puts "I am in Ractor!"} r.take

Ractors do not share usual objects, so the some kind of thread-safety concerns such as data-race, race-conditions are not available on multi-ractor programming.

To achieve this, ractors severely limit object sharing between different ractors. For example, unlike threads, ractors can't access each other's objects, nor any objects through variables of the outer scope.

a = 1 r = Ractor.new {puts "I am in Ractor! a=#{a}"}

On CRuby (the default implementation), Global Virtual Machine Lock (GVL) is held per ractor, so ractors are performed in parallel without locking each other.

Instead of accessing the shared state, the objects should be passed to and from ractors via sending and receiving objects as messages.

a = 1 r = Ractor.new do a_in_ractor = receive puts "I am in Ractor! a=#{a_in_ractor}" end r.send(a)
r.take

There are two pairs of methods for sending/receiving messages:

In addition to that, an argument to Ractor.new would be passed to block and available there as if received by Ractor.receive, and the last block value would be sent outside of the ractor as if sent by Ractor.yield.

A little demonstration on a classic ping-pong:

server = Ractor.new do puts "Server starts: #{self.inspect}" puts "Server sends: ping" Ractor.yield 'ping'
received = Ractor.receive
puts "Server received: #{received}" end

client = Ractor.new(server) do |srv|
puts "Client starts: #{self.inspect}" received = srv.take
puts "Client received from "
"#{srv.inspect}: #{received}" puts "Client sends to "
"#{srv.inspect}: pong" srv.send 'pong'
end

[client, server].each(&:take)

This will output:

Server starts: #<Ractor:#2 test.rb:1 running> Server sends: ping Client starts: #<Ractor:#3 test.rb:8 running> Client received from #<Ractor:#2 rac.rb:1 blocking>: ping Client sends to #<Ractor:#2 rac.rb:1 blocking>: pong Server received: pong

It is said that Ractor receives messages via the incoming port, and sends them to the outgoing port. Either one can be disabled with Ractor#close_incoming and Ractor#close_outgoing respectively. If a ractor terminated, its ports will be closed automatically.

When the object is sent to and from the ractor, it is important to understand whether the object is shareable or unshareable. Most of objects are unshareable objects.

Shareable objects are basically those which can be used by several threads without compromising thread-safety; e.g. immutable ones. Ractor.shareable? allows to check this, and Ractor.make_shareable tries to make object shareable if it is not.

Ractor.shareable?(1)
Ractor.shareable?('foo')
Ractor.shareable?('foo'.freeze)

ary = ['hello', 'world'] ary.frozen?
ary[0].frozen?
Ractor.make_shareable(ary) ary.frozen?
ary[0].frozen?
ary[1].frozen?

When a shareable object is sent (via send or Ractor.yield), no additional processing happens, and it just becomes usable by both ractors. When an unshareable object is sent, it can be either copied or moved. The first is the default, and it makes the object's full copy by deep cloning of non-shareable parts of its structure.

data = ['foo', 'bar'.freeze] r = Ractor.new do data2 = Ractor.receive puts "In ractor: #{data2.object_id}, #{data2[0].object_id}, #{data2[1].object_id}" end r.send(data) r.take puts "Outside : #{data.object_id}, #{data[0].object_id}, #{data[1].object_id}"

This will output:

In ractor: 340, 360, 320 Outside : 380, 400, 320

(Note that object id of both array and non-frozen string inside array have changed inside the ractor, showing it is different objects. But the second array's element, which is a shareable frozen string, has the same object_id.)

Deep cloning of the objects may be slow, and sometimes impossible. Alternatively, move: true may be used on sending. This will move the object to the receiving ractor, making it inaccessible for a sending ractor.

data = ['foo', 'bar'] r = Ractor.new do data_in_ractor = Ractor.receive puts "In ractor: #{data_in_ractor.object_id}, #{data_in_ractor[0].object_id}" end r.send(data, move: true) r.take puts "Outside: moved? #{Ractor::MovedObject === data}" puts "Outside: #{data.inspect}"

This will output:

In ractor: 100, 120 Outside: moved? true test.rb:9:in `method_missing': can not send any methods to a moved object (Ractor::MovedError)

Notice that even inspect (and more basic methods like __id__) is inaccessible on a moved object.

Besides frozen objects, there are shareable objects. Class and Module objects are shareable so the Class/Module definitons are shared between ractors. Ractor objects are also shareable objects. All operations for the shareable mutable objects are thread-safe, so the thread-safety property will be kept. We can not define mutable shareable objects in Ruby, but C extensions can introduce them.

It is prohibited to access instance variables of mutable shareable objects (especially Modules and classes) from ractors other than main:

class C class << self attr_accessor :tricky end end

C.tricky = 'test'

r = Ractor.new(C) do |cls| puts "I see #{cls}" puts "I can't see #{cls.tricky}" end r.take

Ractors can access constants if they are shareable. The main Ractor is the only one that can access non-shareable constants.

GOOD = 'good'.freeze BAD = 'bad'

r = Ractor.new do puts "GOOD=#{GOOD}" puts "BAD=#{BAD}" end r.take

r = Ractor.new do puts "I see #{C}" puts "I can't see #{C.tricky}" end r.take

See also the description of # shareable_constant_value pragma in Comments syntax explanation.

Ractors vs threads ↑

Each ractor creates its own thread. New threads can be created from inside ractor (and, on CRuby, sharing GVL with other threads of this ractor).

r = Ractor.new do a = 1 Thread.new {puts "Thread in ractor: a=#{a}"}.join end r.take

Note on code examples ↑

In examples below, sometimes we use the following method to wait till ractors that are not currently blocked will finish (or process till next blocking) method.

def wait sleep(0.1) end

It is **only for demonstration purposes** and shouldn't be used in a real code. Most of the times, just take is used to wait till ractor will finish.

Reference ↑

See Ractor desgin doc for more details.

Public Class Methods

count() click to toggle source

Returns total count of Ractors currently running.

Ractor.count
r = Ractor.new(name: 'example') { Ractor.yield(1) } Ractor.count
r.take
r.take
Ractor.count

def self.count __builtin_cexpr! %q{ ULONG2NUM(GET_VM()->ractor.cnt); } end

current() click to toggle source

Returns the currently executing Ractor.

Ractor.current

def self.current __builtin_cexpr! %q{ rb_ractor_self(rb_ec_ractor_ptr(ec)); } end

main() click to toggle source

returns main ractor

def self.main __builtin_cexpr! %q{ rb_ractor_self(GET_VM()->ractor.main_ractor); } end

new(*args, name: nil) {|*args| block } → ractor click to toggle source

Create a new Ractor with args and a block.

A block (Proc) will be isolated (can't access to outer variables). self inside the block will refer to the current Ractor.

r = Ractor.new { puts "Hi, I am #{self.inspect}" } r.take

args passed to the method would be propagated to block args by the same rules as objects passed through send/Ractor.receive: if args are not shareable, they will be copied (via deep cloning, which might be inefficient).

arg = [1, 2, 3] puts "Passing: #{arg} (##{arg.object_id})" r = Ractor.new(arg) {|received_arg| puts "Received: #{received_arg} (##{received_arg.object_id})" } r.take

Ractor's name can be set for debugging purposes:

r = Ractor.new(name: 'my ractor') {} p r

def self.new(*args, name: nil, &block) b = block raise ArgumentError, "must be called with a block" unless block loc = caller_locations(1, 1).first loc = "#{loc.path}:#{loc.lineno}" __builtin_ractor_create(loc, name, args, b) end

receive → msg click to toggle source

Receive an incoming message from the current Ractor's incoming port's queue, which was sent there by send.

r = Ractor.new do v1 = Ractor.receive puts "Received: #{v1}" end r.send('message1') r.take

Alternatively, private instance method receive may be used:

r = Ractor.new do v1 = receive puts "Received: #{v1}" end r.send('message1') r.take

The method blocks if the queue is empty.

r = Ractor.new do puts "Before first receive" v1 = Ractor.receive puts "Received: #{v1}" v2 = Ractor.receive puts "Received: #{v2}" end wait puts "Still not received" r.send('message1') wait puts "Still received only one" r.send('message2') r.take

Output:

Before first receive Still not received Received: message1 Still received only one Received: message2

If close_incoming was called on the ractor, the method raises Ractor::ClosedError if there are no more messages in incoming queue:

Ractor.new do close_incoming receive end wait

def self.receive __builtin_cexpr! %q{ ractor_receive(ec, rb_ec_ractor_ptr(ec)) } end

Also aliased as: recv

receive_if {|msg| block } → msg click to toggle source

Receive only a specific message.

Instead of Ractor.receive, Ractor.receive_if can provide a pattern by a block and you can choose the receiving message.

r = Ractor.new do p Ractor.receive_if{|msg| msg.match?(/foo/)} p Ractor.receive_if{|msg| msg.match?(/bar/)} p Ractor.receive_if{|msg| msg.match?(/baz/)} end r << "bar1" r << "baz2" r << "foo3" r.take

This will output:

foo3 bar1 baz2

If the block returns a truthy value, the message will be removed from the incoming queue and returned. Otherwise, the messsage remains in the incoming queue and the following received messages are checked by the given block.

If there are no messages left in the incoming queue, the method will block until new messages arrive.

If the block is escaped by break/return/exception/throw, the message is removed from the incoming queue as if a truthy value had been returned.

r = Ractor.new do val = Ractor.receive_if{|msg| msg.is_a?(Array)} puts "Received successfully: #{val}" end

r.send(1) r.send('test') wait puts "2 non-matching sent, nothing received" r.send([1, 2, 3]) wait

Prints:

2 non-matching sent, nothing received Received successfully: [1, 2, 3]

Note that you can not call receive/receive_if in the given block recursively. It means that you should not do any tasks in the block.

Ractor.current << true Ractor.receive_if{|msg| Ractor.receive}

def self.receive_if &b Primitive.ractor_receive_if b end

select(*ractors, [yield_value:, move: false]) → [ractor or symbol, obj] click to toggle source

Waits for the first ractor to have something in its outgoing port, reads from this ractor, and returns that ractor and the object received.

r1 = Ractor.new {Ractor.yield 'from 1'} r2 = Ractor.new {Ractor.yield 'from 2'}

r, obj = Ractor.select(r1, r2)

puts "received #{obj.inspect} from #{r.inspect}"

If one of the given ractors is the current ractor, and it would be selected, r will contain :receive symbol instead of the ractor object.

r1 = Ractor.new(Ractor.current) do |main| main.send 'to main' Ractor.yield 'from 1' end r2 = Ractor.new do Ractor.yield 'from 2' end

r, obj = Ractor.select(r1, r2, Ractor.current) puts "received #{obj.inspect} from #{r.inspect}"

If yield_value is provided, that value may be yielded if another Ractor is calling take. In this case, the pair [:yield, nil] would be returned:

r1 = Ractor.new(Ractor.current) do |main| puts "Received from main: #{main.take}" end

puts "Trying to select" r, obj = Ractor.select(r1, Ractor.current, yield_value: 123) wait puts "Received #{obj.inspect} from #{r.inspect}"

This will print:

Trying to select Received from main: 123 Received nil from :yield

move boolean flag defines whether yielded value should be copied (default) or moved.

def self.select(*ractors, yield_value: yield_unspecified = true, move: false) raise ArgumentError, 'specify at least one ractor or yield_value' if yield_unspecified && ractors.empty?

__builtin_cstmt! %q{ const VALUE *rs = RARRAY_CONST_PTR_TRANSIENT(ractors); VALUE rv; VALUE v = ractor_select(ec, rs, RARRAY_LENINT(ractors), yield_unspecified == Qtrue ? Qundef : yield_value, (bool)RTEST(move) ? true : false, &rv); return rb_ary_new_from_args(2, rv, v); } end

yield(msg, move: false) → nil click to toggle source

Send a message to the current ractor's outgoing port to be consumed by take.

r = Ractor.new {Ractor.yield 'Hello from ractor'} puts r.take

The method is blocking, and will return only when somebody consumes the sent message.

r = Ractor.new do Ractor.yield 'Hello from ractor' puts "Ractor: after yield" end wait puts "Still not taken" puts r.take

This will print:

Still not taken Hello from ractor Ractor: after yield

If the outgoing port was closed with close_outgoing, the method will raise:

r = Ractor.new do close_outgoing Ractor.yield 'Hello from ractor' end wait

The meaning of move argument is the same as for send.

def self.yield(obj, move: false) __builtin_cexpr! %q{ ractor_yield(ec, rb_ec_ractor_ptr(ec), obj, move) } end

Public Instance Methods

[](sym) click to toggle source

get a value from ractor-local storage

def Primitive.ractor_local_value(sym) end

[]=(sym, val) click to toggle source

set a value in ractor-local storage

def []=(sym, val) Primitive.ractor_local_value_set(sym, val) end

close_incoming → true | false click to toggle source

Closes the incoming port and returns its previous state. All further attempts to Ractor.receive in the ractor, and send to the ractor will fail with Ractor::ClosedError.

r = Ractor.new {sleep(500)} r.close_incoming
r.close_incoming
r.send('test')

def close_incoming __builtin_cexpr! %q{ ractor_close_incoming(ec, RACTOR_PTR(self)); } end

close_outgoing → true | false click to toggle source

Closes the outgoing port and returns its previous state. All further attempts to Ractor.yield in the ractor, and take from the ractor will fail with Ractor::ClosedError.

r = Ractor.new {sleep(500)} r.close_outgoing
r.close_outgoing
r.take

def close_outgoing __builtin_cexpr! %q{ ractor_close_outgoing(ec, RACTOR_PTR(self)); } end

inspect() click to toggle source

def inspect loc = __builtin_cexpr! %q{ RACTOR_PTR(self)->loc } name = __builtin_cexpr! %q{ RACTOR_PTR(self)->name } id = __builtin_cexpr! %q{ INT2FIX(rb_ractor_id(RACTOR_PTR(self))) } status = _builtin_cexpr! %q{ rb_str_new2(ractor_status_str(RACTOR_PTR(self)->status)) } "#<Ractor:##{id}#{name ? ' '+name : ''}#{loc ? " " + loc : ''} #{status}>" end

Also aliased as: to_s

name() click to toggle source

The name set in Ractor.new, or nil.

def name __builtin_cexpr! %q{RACTOR_PTR(self)->name} end

send(msg, move: false) → self click to toggle source

Send a message to a Ractor's incoming queue to be consumed by Ractor.receive.

r = Ractor.new do value = Ractor.receive puts "Received #{value}" end r.send 'message'

The method is non-blocking (will return immediately even if the ractor is not ready to receive anything):

r = Ractor.new {sleep(5)} r.send('test') puts "Sent successfully"

Attempt to send to ractor which already finished its execution will raise Ractor::ClosedError.

r = Ractor.new {} r.take p r

r.send('test')

If close_incoming was called on the ractor, the method also raises Ractor::ClosedError.

r = Ractor.new do sleep(500) receive end r.close_incoming r.send('test')

If the obj is unshareable, by default it would be copied into ractor by deep cloning. If the move: true is passed, object is moved into ractor and becomes inaccessible to sender.

r = Ractor.new {puts "Received: #{receive}"} msg = 'message' r.send(msg, move: true) r.take p msg

This prints:

Received: message in p': undefined method inspect' for #Ractor::MovedObject:0x000055c99b9b69b8

All references to the object and its parts will become invalid in sender.

r = Ractor.new {puts "Received: #{receive}"} s = 'message' ary = [s] copy = ary.dup r.send(ary, move: true)

s.inspect

ary.class

copy.class

copy[0].inspect

If the object was shareable, move: true has no effect on it:

r = Ractor.new {puts "Received: #{receive}"} s = 'message'.freeze r.send(s, move: true) s.inspect

def send(obj, move: false) __builtin_cexpr! %q{ ractor_send(ec, RACTOR_PTR(self), obj, move) } end

Also aliased as: <<

take → msg click to toggle source

Take a message from ractor's outgoing port, which was put there by Ractor.yield or at ractor's finalization.

r = Ractor.new do Ractor.yield 'explicit yield' 'last value' end puts r.take puts r.take puts r.take

The fact that the last value is also put to outgoing port means that take can be used as some analog of Thread#join (“just wait till ractor finishes”), but don't forget it will raise if somebody had already consumed everything ractor have produced.

If the outgoing port was closed with close_outgoing, the method will raise Ractor::ClosedError.

r = Ractor.new do sleep(500) Ractor.yield 'Hello from ractor' end r.close_outgoing r.take

If an uncaught exception is raised in the Ractor, it is propagated on take as a Ractor::RemoteError.

r = Ractor.new {raise "Something weird happened"}

begin r.take rescue => e p e
p e.ractor == r
p e.cause
end

Ractor::ClosedError is a descendant of StopIteration, so the closing of the ractor will break the loops without propagating the error:

r = Ractor.new do 3.times {|i| Ractor.yield "message #{i}"} "finishing" end

loop {puts "Received: " + r.take} puts "Continue successfully"

This will print:

Received: message 0 Received: message 1 Received: message 2 Received: finishing Continue successfully

def take __builtin_cexpr! %q{ ractor_take(ec, RACTOR_PTR(self)) } end

Private Instance Methods

receive() click to toggle source

same as Ractor.receive

    def receive

__builtin_cexpr! %q{ ractor_receive(ec, rb_ec_ractor_ptr(ec)) } end

Also aliased as: recv

receive_if(&b) click to toggle source 

    def receive_if &b

Primitive.ractor_receive_if b end